The present invention deals with power machines such as skid steer loaders. More particularly, the present invention deals with control systems in such power machines.
Power machines, such as skid steer loaders, typically have a frame which supports a cab or operator compartment and a movable lift arm which, in turn, supports a work tool such as a bucket. The movable lift arm is pivotably coupled to the frame of the skid steer loader and is powered by power actuators which are commonly hydraulic cylinders. In addition, the tool is coupled to the lift arm and is powered by one or more additional power actuators which are also commonly hydraulic cylinders. An operator manipulating a skid steer loader raises and lowers the lift arm, and manipulates the tool, by actuating the hydraulic cylinders coupled to the lift arm, and the hydraulic cylinder coupled to the tool.
Skid steer loaders also commonly have an engine which drives a hydraulic pump. The hydraulic pump powers hydraulic traction motors which provide powered movement of the skid steer loader. The traction motors are commonly coupled to the wheels through a drive mechanism such as a chain drive.
Front attachments, such as augers or angle brooms, typically include their own hydraulic drive motors and are attachable or mountable to the lift arm. An auxiliary hydraulic system is used to control the flow of hydraulic fluid between a hydraulic pump on the loader and the hydraulic motor on the front mounted attachment. In one known system, the flow of hydraulic fluid to the motor on a front mounted attachment is controlled by an electronic control valve which is operated in an either fully opened or fully closed fashion. In other words, if the operator actuates an operator input, a signal is provided to a solenoid on the electronic control valve either opening or closing the control valve to either provide, or discontinue, full flow of hydraulic fluid to the hydraulic motor on the front mounted attachment.
In addition, rear mounted attachments, such as stabilizers, are commonly attached or mounted to a rear portion of the loader. The rear mounted attachments also typically include their own hydraulic motors and are also supplied with hydraulic fluid from a pump which is controlled by an auxiliary hydraulic system on the loader.
In one prior skid steer loader, only a single auxiliary hydraulic power circuit is provided and a diverter valve is provided to route hydraulic fluid from the front mounted attachment to the rear mounted attachment. Thus, either the front or rear mounted attachment is operable at one time. In another prior loader, the auxiliary hydraulic power circuit is configured to allow simultaneous operation of both front and rear mounted attachments.
It is also common for control levers in skid steer loaders to have hand grips which support a plurality of buttons or actuable switches, actuable by the operator to perform certain functions. Depending upon the particular type of attachment or attachments mounted on the skid steer loader, certain functions may be disabled or unusable. Further, depending upon the particular type of attachment or attachments mounted on the skid steer loader, certain combinations of inputs from the operator input devices, when performed simultaneously, can result in opposing control valves being opened. This essentially provides an equal amount of pressurized fluid to both sides of a hydraulic actuator or hydraulic motor.
There is a continuing need for improved hydraulic control systems in such power machines to enhance performance of the machines.